High efficient power electronic devices (also referred to as power switch devices) are of significant application value in domains such as smart grids, industrial controlling, new energy power generation, electric vehicles, and consumer electronics, etc. Globally, more than 70% of power electronic systems are manipulated and administrated by power administration systems based on power semiconductor devices. Performance of conventional Si power electronic devices approaches to physical limit of Si semiconductor materials. Novel type of wide forbidden-band semiconductor devices, such as SiC and GaN, have higher breakdown electric field value, higher operation frequency and even lower on-resistance, and thus have already become promising candidates for the next generation of high efficient power electronics.
Enhancement-mode is essential for safe operation of power electronic devices, which ensures safety of the devices even without gate control when it is operated under high voltage, and will not cause damages of the system. For this reason, the power electronic devices have to be enhancement-mode (also referred to as normally-off) devices, that is, thresholds for the devices must be above 0V. Currently, GaN-based enhancement-mode power electronic devices are mainly manufactured on the basis of Al(In,Ga)N/GaN heterostructures, in which, relying on strong spontaneous piezoelectric polarization effect between Al(In,Ga)N barrier layers and GaN buffer layers, a two-dimensional electron gas (2 DEG) with a density of up to 1013 cm−2 will be induced in channels of Al(In,Ga)N/GaN heterostructures. Therefore, GaN-based power electronic devices which are manufactured based on such structures (including HEMTs and MIS-HEMTs) are generally depletion-type. Several kinds of techniques are world-widely used to realize GaN-based enhancement-mode devices, mainly comprising: 1) thinning the Al(In,Ga)N barrier layer by gate trench etching; 2) injecting negative fluoride ions into the Al(In,Ga)N barrier layer; 3) growing a P—(Al)GaN cap layer on surface of the barrier layer; 4) growing a InGaN or thick GaN anti-polarization layer on surface of the barrier layer; 5) a cascode configuration of enhancement-mode Si-MOSFET and GaN-based depleted HEMT/MIS-HEMT.
The P—(Al)GaN cap layer technique depletes the 2 DEG in a channel of the Al(In,Ga)N/GaN heterostructure by utilizing the space-charge region effect of a PN-junction, so as to implement the enhancement-mode. It continues to in-situ epitaxial grow a P—(Al)GaN cap layer on the Al(In,Ga)N/GaN heterostructures by means of Metal Organic Chemical Vapor Deposition (MOCVD) or molecular beam epitaxy (MBE). The epitaxial technique can provide accurate control on thickness and uniformity, therefore, a fine threshold consistency may be generally obtained when the P—(Al)GaN technique is adopted. Specifically, exemplary products for P—(Al)GaN technique have been reported by manufactures such as Efficient Power Conversion Corporation (EPC) in US, Panasonic in Japan, Samsung in Korea, GaN Systems in Canada, and TSMC in Taiwan.
Although the P—(Al)GaN cap layer technique has raised the threshold for GaN-based enhancement-mode device to +1.5 V, when gate voltage is above forward turn-on voltage for the PN junction, forward leakage for the gate will increases very quickly, and will possibly lead to breakdown of the gate, and thus affect safety of the device. Therefore, in order to promote application and industrialization of the P—(Al)GaN cap layer technique in the GaN-based Power electronics, it is essential to develop a gate leakage inhibition technique on the basis of the P—(Al)GaN cap layer.
In addition, because of the presence of the surface state, GaN-based power electronic device may exhibit serious current collapse phenomenon when it is operated at high voltage, which directly leads to increase of dynamic on-resistance and power consumption of the device. Researches have shown that such a surface state can hardly be completely avoided. Therefore, it will be more applicable to develop a technique for facilitating fast recovery of the surface state and thus avoid the hard nut of dealing with the surface state.
However, the above electronic device cannot meet requirements for electronic devices due to its low gate leakage performance, and it also needs to catch up with the strict standard on the aspect of threshold control ability including self-repairing of current collapse.